Packaging a server backend along with a minimal kernel and V8 VM isn't any more complicated than most of the build tools used today.

Here are the specifics: http://node-os.com/GitBlog/article.html#!200

When you cut 99% of the crap out of an OS, it becomes a lot easier to package/distribute.

Most of the work on NodeOS has to do with replacing POSIX with Javascript equivalents.

Immutable operating systems aren't a new idea either. How you think a Linux LiveCD works? ChromeOS is basically an immutable OS with an added persistence layer.

There's a lot more work to be done before any of the Unikernel implementations (ie NodeOS isn't the only one) are ready for production.

With that said, for webservers that aren't required to persist any state locally, it makes sense to remove mutability -- and there fore OS-level security vulnerabilities -- as a concern. That way, devs have more time/resources to focus on app-level security.